Method for dividing workpieces composed of brittle-hard materials and elements producible by the method

Abstract

A method for dividing a workpiece into elements includes: a pulsed laser beam of an ultrashort pulse laser is directed onto a workpiece composed of brittle-hard material; instances of filamentary damage are introduced next to one another along a path. The distance between the instances of filamentary damage at least in one portion of the path is selected such that one of the following conditions is met: (i) the difference in terms of magnitude between the characteristic fracture strengths of the element upon bending in opposite directions in this portion is at most 10 MPa; (ii) the difference in terms of magnitude between the characteristic fracture strengths of the element upon bending in opposite directions in this portion is at least 30 MPa; and (iii) the difference in terms of magnitude between the fracture strengths upon bending of the element in opposite directions is at least 30 MPa*d[mm]*π/3.

What is claimed is: 
     
         1 . A method for dividing a workpiece into a plurality of elements, the method comprising the steps of:
 providing the workpiece which is composed of a material which is brittle-hard;   directing a laser beam—which is pulsed—of an ultrashort pulse laser onto the workpiece;   coordinating a wavelength of the laser beam and the material of the workpiece with one another such that the workpiece is substantially transparent to the laser beam;   focusing the laser beam to a focus which is elongate in a beam direction and which at least partially lies within the workpiece, wherein an intensity of the laser beam and an extent of the focus are so great that the laser beam leaves behind a first filamentary damage in the workpiece;   introducing a plurality of instances of filamentary damage—which includes the first filamentary damage—next to one another along a path, wherein the plurality of instances of filamentary damage extend from a first surface of the workpiece at which the laser beam enters to a second surface—which is opposite the first surface—of the workpiece at which the laser beam exits again;   separating the workpiece along the path, such that at least two of the plurality of elements are obtained as a result of the separating, the at least two of the plurality of elements including the first surface, the second surface, and an edge surface which is formed by the separating and which connects the first surface and the second surface;   selecting, when introducing the plurality of instances of filamentary damage, a distance between adjacent ones of the plurality of instances of filamentary damage at least in a portion of the path such that one of the following conditions is met:
 (i) a difference in terms of a magnitude between a plurality of characteristic fracture strengths of a respective one of the at least two of the plurality of elements upon bending in opposite directions in the portion of the path is at most 10 MPa; 
 (ii) a difference in terms of a magnitude between a plurality of characteristic fracture strengths of a respective one of the at least two of the plurality of elements upon bending in opposite directions in the portion of the path is at least 30 MPa; and 
 (iii) a difference in terms of a magnitude between a plurality of fracture strengths of a respective one of the at least two of the plurality of elements upon bending in opposite directions is at least 30 MPa*d[mm]*π/3. 
   
     
     
         2 . The method according to  claim 1 , wherein, when introducing the plurality of instances of filamentary damage, the distance between adjacent ones of the plurality of instances of filamentary damage at least in the portion of the path is selected such that at least one of the following conditions is met:
 (i) a B10 value of a Weibull distribution of a plurality of fracture strengths upon bending of the respective one of the at least two of the plurality of elements is at least 60 MPa, for a plurality of tensile stresses on both the first surface and the second surface;   (ii) a characteristic fracture strength value of a Weibull distribution upon bending of the respective one of the at least two of the plurality of elements is at least 80 MPa, for a tensile stress on both the first surface and the second surface; and   (iii) a difference in terms of a magnitude between a plurality of B10 values of a Weibull distribution of a plurality of fracture strengths upon bending of the respective one of the at least two of the plurality of elements in opposite directions is either at most 5 MPa or at least 30 MPa.   
     
     
         3 . The method according to  claim 1 , wherein a setting of a fracture strength of the respective one of the at least two of the plurality of elements includes at least one of the following steps:
 increasing the fracture strength of the second surface at which the laser beam exits by increasing the distance between adjacent ones of the plurality of instances of filamentary damage; and   increasing the fracture strength of the first surface at which the laser beam enters by reducing the distance between adjacent ones of the plurality of instances of filamentary damage.   
     
     
         4 . The method according to  claim 1 , wherein the distance between adjacent ones of the plurality of instances of filamentary damage is set in a range of 1 μm to 16 μm. 
     
     
         5 . The method according to  claim 1 , wherein a focal line, along which the intensity exceeds 10 13  W/cm 2 , is generated from the laser beam by beam shaping, wherein a maximum value of the intensity deviates by at least 10% from an average value of the intensity along the focal line. 
     
     
         6 . The method according to  claim 1 , wherein the laser beam is focused by way of a lens with a spherical aberration. 
     
     
         7 . The method according to  claim 1 , wherein the plurality of elements includes a first element and a second element, wherein the first element is a glass ribbon and is produced by separating a plurality of borders of a raw glass ribbon, wherein the separating of the plurality of borders includes (a) introducing the plurality of instances of filamentary damage along a plurality of the path which extend parallel to a plurality of longitudinal edges of the raw glass ribbon and (b) fracturing the plurality of borders, wherein the glass ribbon is rolled up and thereby forms a roll, wherein a plurality of distances between the plurality of instances of filamentary damage are selected such that the first surface—which forms an outer side of the roll of the glass ribbon—has a higher fracture strength than the second surface which forms an inner side of the roll. 
     
     
         8 . The method according to  claim 1 , wherein the plurality of elements includes a first element and a second element, wherein the plurality of instances of filamentary damage are introduced at different distances along certain portions of the path, such that, after the step of separating, the first element is obtained which includes the edge surface having a plurality of portions which differ with regard to a distance between adjacent ones of the plurality of instances of filamentary damage and a plurality of characteristic fracture strengths of the first surface and the second surface upon bending of the first element in a respective one of the plurality of portions of the edge surface. 
     
     
         9 . The method according to  claim 1 , wherein a distance between adjacent ones of the plurality of instances of filamentary damage is set such that a Weibull modulus of a strength distribution of at least one of the first surface and the second surface is greater than 6. 
     
     
         10 . The method according to  claim 1 , wherein the step of separating occurs by exerting a mechanical stress. 
     
     
         11 . An element composed of a material which is brittle-hard, the element comprising:
 a first surface;   a second surface which is opposite the first surface;   an edge surface which connects the first surface and the second surface, the edge surface being a fracture surface, the fracture surface including a plurality of instances of filamentary damage, which run at regular distances and parallel to one another at least in a first portion of the edge surface;   a first edge, which forms a transition between the edge surface and the first surface or the second surface;   a second edge which is opposite the first edge,   wherein one of the following features is specified for a fracture strength of the element at the edge surface which is formed as the fracture surface:
 (i) a difference in terms of a magnitude between a plurality of characteristic fracture strengths of the element upon bending in opposite directions in the first portion of the edge surface is at most 5 MPa; 
 (ii) a difference in terms of a magnitude between a plurality of characteristic fracture strengths of the element upon bending in opposite directions in the first portion of the edge surface is at least 30 MPa; and 
 (iii) a difference in terms of a magnitude between a plurality of fracture strengths upon bending of the element in opposite directions is at least 30 MPa*d[mm]*π/3. 
   
     
     
         12 . The element according to  claim 11 , wherein at least one of the following features is specified for the fracture strength of the element:
 (i) a B10 value of a Weibull distribution of the fracture strengths upon bending of the element is at least 60 MPa for a plurality of tensile stresses on both the first surface and the second surface;   (ii) a difference in terms of a magnitude between a plurality of B10 values of a Weibull distribution of a plurality of fracture strengths upon bending of the element in opposite directions is at most 5 MPa.   
     
     
         13 . The element according to  claim 11 , wherein a first distance between the plurality of instances of filamentary damage lies in a range of 1 μm to 16 μm, the regular distances including the first distance. 
     
     
         14 . The element according to  claim 11 , wherein a first distance between the plurality of instances of filamentary damage is such that a Weibull modulus for the fracture strength of the first surface and the second surface is greater than 6, the regular distances including the first distance. 
     
     
         15 . The element according to  claim 11 , wherein the edge surface has a plurality of portions which include the first portion and which differ with regard to a first distance between the plurality of instances of filamentary damage and a plurality of characteristic fracture strengths of the first surface and the second surface upon bending of the element in a respective one of the plurality of portions of the edge surface, the regular distances including the first distance. 
     
     
         16 . The element according to  claim 15 , wherein the element is bent in at least one of the plurality of portions of the edge surface such that the first surface or the second surface having a higher characteristic fracture strength relative to the other of the first surface or the second surface is under a tensile stress on account of the element being bent. 
     
     
         17 . The element according to  claim 11 , wherein the edge surface—which is formed as the fracture surface—has a surface proportion of smooth fracture regions of less than 10%. 
     
     
         18 . The element according to  claim 11 , wherein the element is:
 a lens;   an eyepiece or a constituent part of an eyepiece;   a rolled-up glass ribbon;   a cover glass configured for a mobile display;   a glass tube or a container glass;   a glass ceramic hob; or   a glass element which is coated on one side.   
     
     
         19 . The element according to  claim 18 , wherein the glass element has a biochemically active layer for immobilizing proteins, wherein the first surface or the second surface—which is loaded during a processing—has a higher fracture strength than the other of the first surface or the second surface. 
     
     
         20 . The element according to  claim 11 , wherein the element is configured for being produced according to a method for dividing a workpiece into a plurality of the element, the method including the steps of:
 providing the workpiece which is composed of the material which is brittle-hard;   directing a laser beam—which is pulsed—of an ultrashort pulse laser onto the workpiece;   coordinating a wavelength of the laser beam and the material of the workpiece with one another such that the workpiece is substantially transparent to the laser beam;   focusing the laser beam to a focus which is elongate in a beam direction and which at least partially lies within the workpiece, wherein an intensity of the laser beam and an extent of the focus are so great that the laser beam leaves behind a first filamentary damage in the workpiece;   introducing the plurality of instances of filamentary damage—which includes the first filamentary damage—next to one another along a path, wherein the plurality of instances of filamentary damage extend from the first surface of the workpiece at which the laser beam enters to the second surface—which is opposite the first surface—of the workpiece at which the laser beam exits again;   separating the workpiece along the path, such that at least two of the plurality of the element are obtained as a result of the separating, the at least two of the plurality of the element including the first surface, the second surface, and the edge surface which is formed by the separating and which connects the first surface and the second surface;   selecting, when introducing the plurality of instances of filamentary damage, a distance between adjacent ones of the plurality of instances of filamentary damage at least in a portion of the path such that one of the following conditions is met:
 (i) a difference in terms of a magnitude between a plurality of characteristic fracture strengths of a respective one of the at least two of the plurality of the element upon bending in opposite directions in the portion of the path is at most 10 MPa; 
 (ii) a difference in terms of a magnitude between a plurality of characteristic fracture strengths of a respective one of the at least two of the plurality of the element upon bending in opposite directions in the portion of the path is at least 30 MPa; and 
 (iii) a difference in terms of a magnitude between a plurality of fracture strengths of a respective one of the at least two of the plurality of the element upon bending in opposite directions is at least 30 MPa*d[mm]*π/3.